std::sort doesn't work

[cl333r]

Folks can anyone please make this sorting example work? It compiles and runs, but doesn't actually sort the elements from the vector.. I spent a few hours and can't figure out what's the matter..

main.cpp:


#include <stdlib.h>
#include <iostream>
#include <vector>
#include <algorithm>
#include "Person.h"

using namespace std;

int main(int argc, char** argv) {

Person *p1 = new Person( "James" );
Person *p2 = new Person( "Brian" );
Person *p3 = new Person( "John" );
Person *p4 = new Person( "Mark" );

vector<Person*> v;
v.push_back(p1);
v.push_back(p2);
v.push_back(p3);
v.push_back(p4);

std::sort(v.begin(), v.end());

cout << "Sorted: " << endl;

for( int i=0; i<v.size(); i++) {
Person *p = v.at(i);
cout << p->getName() << endl;
}

return (EXIT_SUCCESS);
}


Person.h:


#ifndef _PERSON_H
#define _PERSON_H

#include <iostream>
#include <glibmm.h>
using namespace std;

class Person {
public:
Person(Glib::ustring);
virtual ~Person();
Glib::ustring getName();

bool operator<(Person* other) {
cout << "called operator < for" << getName() << endl;
return other->getName().compare(name) > 0;
}
protected:
Glib::ustring name;
};
#endif


Person.cpp:


#include "Person.h"

Person::Person(Glib::ustring s) {
name=s;
}

Person::~Person() {}

Glib::ustring Person::getName() {
return name;
}

[dwhitney67]

Of course it is working! You are sorting the pointers to the Person object you allocated.

But I bet that is not what you intended... you probably wanted the Person objects to be sorted within the vector by the Person's name attribute.

With your design, define a function like:


bool nameSort(const Person* one, const Person* two)
{
return one->getName().compare(two.getName()) < 0;
}

Note, this is not a class method of Person, but a free-floating function.

Then in your main() code:


...
std::sort(v.begin, v.end(), nameSort);
...


P.S. The string passed to the constructor should be defined as "const Glib::ustring&", and the getName() method should be defined as "Glib::ustring getName() const".

[cl333r]

Thanks a lot! It works now.
My final classes:

main.cpp:


#include <stdlib.h>
#include <iostream>
#include <vector>
#include <algorithm>
#include "Person.h"

using namespace std;

bool nameSort(const Person* one, const Person* two)
{
return one->getName().compare(two->getName()) < 0;
}

int main(int argc, char** argv) {

Person *p1 = new Person( "James" );
Person *p2 = new Person( "Brian" );
Person *p3 = new Person( "John" );
Person *p4 = new Person( "Mark" );

vector<Person*> v;
v.push_back(p1);
v.push_back(p2);
v.push_back(p3);
v.push_back(p4);

std::sort(v.begin(), v.end(), nameSort);

cout << "Sorted: " << endl;

for( int i=0; i<v.size(); i++) {
Person *p = v.at(i);
cout << p->getName() << endl;
}

return (EXIT_SUCCESS);
}


Person.h:


#ifndef _PERSON_H
#define _PERSON_H

#include <iostream>
#include <glibmm.h>
using namespace std;

class Person {
public:
Person(const Glib::ustring& );
virtual ~Person();
Glib::ustring getName() const;
protected:
Glib::ustring name;
};

#endif


Person.cpp:


#include "Person.h"

Person::Person(const Glib::ustring& s) {
name=s;
}

Person::~Person() {}

Glib::ustring Person::getName() const {
return name;
}